# Resource Maps

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## What is a resource?

Resources are the building blocks of an SCI game. Graphics, sounds, animations, scripts, etc. are all resources. In SCI there are 18 resource types: view, picture, script, text, sound, memory, vocabulary, font, cursor, patch, bitmap, palette, cdaudio, audio, sync(?), message, map, and heap. I believe that some of these were only introduced later with the SCI1 engine, meaning that not all of them are available in an SCI0 game.

## About the resource map

The SCI interpreter needs some way of organizing the individual resources. The way Sierra accomplished this was through a file known as resource.map The resource map is merely a listing of all resources which make up a game. The resources themselves are stored in what I call resource packages. These are the familiar files with names like resource.001 and resource.002.

## The resource.map format

Resource maps are just a bunch of 6 byte structures in a row. The last structure is set to FFFFFFFFFFFF and signifies the end of the file. All other structures list a resource and its location. The structures have the format:

- Resource Identifier (2 bytes)
  - 11 bit resource number (bits 00-10)
  - 5 bit resource type (bits 11-15)
- Resource Location (4 bytes)
  - 26 bit file offset (bits 00-25)
  - 6 bit package number (bits 26-31)

The four fields (resource type, resource number, package number, file offset) are meaningful individually, but may also be grouped in pairs as the list shows.

The resource type is the numerical value (0-17) for one of the 18 resource types previously listed. The resource number is used to name individual resources of the same type. (eg, view.000 through view.032) The interesting thing is that the same resource may be listed multiple times. In the early SCI days it was still possible to play the game straight off the floppy disks. To prevent excessive disk swapping, Sierra put the same resource in multiple resource packages. Each resource will have a listing for each of its instances. The resource type and resource number combine to form a 16 bit resource identifier.

A word about nomenclature: Carl Muckenhoupt used the name "file number" instead of "resource number" in his SCI Decoder. When resources are saved individually, they get saved as type.number, like script.000. I made the change because I think the term "resource number" is clearer. The lurking danger with this is possible confusion between a resource's number and its identifier. I will retain the naming system whenever talking about about a resource as an individual file, but I will continue to call its extension the resource number.

The package number is the extension for the resource package containing the resource. A resource listed with package number 1 would be found in resource.001. The file offset is merely the offset in bytes of the listed resource in the resource package. The package number and file offset combine to form a 32 bit location which completely describes how to find the resource.

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